Modern day aircraft, and particularly modern day military aircraft, typically make use of a large number of actuators, sensors, modules and other components. These components produce, or can be monitored to obtain, signals indicative of their performance during takeoff, landing and other aircraft flight phases. Often one or more aircraft components are monitored and/or controlled by a module called a “line-replaceable-unit” (LRU). An LRU is a highly complex module often incorporating several processors for controlling and/or monitoring one or more components or subassemblies of an aircraft. An LRU may be provided to monitor and/or control one or more external devices such as an actuator, valve, motor, etc., associated with a particular component or assembly of the aircraft. An LRU typically also generates output signals which can be monitored to determine if the LRU and/or the component with which it is associated is not operating properly. Examples of some of the LRU's associated with a C-17 aircraft are listed as follows to provide an appreciation as to the wide ranging and diverse functions of a typical military aircraft which the LRU's are responsible for controlling:
System/ComponentAcronymEmergency Egress SequencerESAerial Delivery Locks Control PanelADLCPCargo Delivery System Control-Status PanelCDSCSPAerial Delivery System ControllerADSCAircraft Fault-Function Indicator PanelAFFIPSensor Signal InterfaceSSIAntiskid-Brake Temperature Monitor Control UnitABTMCUElectronic Engine ControlEECElectronic Engine Control (for Auxiliary EECEECPower)Auxiliary Power Unit Control PanelAPUCPEnvironmental System-Fire Detection Control PanelESFDCPTemperature Control PanelTCPEnvironmental Control System ControllerECSCManifold Failure Detection ControllerMFDCCabin Pressure ControllerCPCCabin Air Pressure Selector PanelCAPSPWindshield Anti-icing Control BoxWAICBWindow Defogging Control BoxWDCBBattery Chargerno acronymGenerator ControlGCElectrical System Control PanelECP(Electrical Control Panel)Static Frequency Converterno acronym(60 Hertz Converter)Static Power Inverterno acronymBus Power Control UnitBPCUHi-Intensity Wingtip Lights Power Supplyno acronymUpper & Lower Beacon Light Power Supplyno acronymPower Supply-Dimming Unitno acronymBattery Charger Setno acronym(Emergency Lighting Battery/Charger)Hydraulic System ControllerHSCHydraulic System Control PanelHSCPFuel System-Engine Start Control PanelFSESCPLiquid Quantity IndicatorLQIGround Refueling Control PanelGRCPFuel Quantity ComputerFQCFluid Purity ControllerFPCBearing-Distance-Heading Indicatorno acronymEngine-Thrust Rating Panel DisplayETRPDSignal Data Recorderno acronym(Quick Access Recorder)(QAR)Standard Flight Data RecorderSFDRPropulsion Data Management ComputerPDMC(Aircraft Propulsion Data Management Computer)(APDMC) (APM)Flight Control ComputerFCCActuator Flight Control PanelAFCPAutomatic Pilot Control-IndicatorAPCIGround Proximity Warning Control PanelGPWCPSpoiler Control-Electronic Flap ComputerSCEFCDisplay UnitDU(Multi Function Display)(MFD)Multifunction Control PanelMCPAir Data ComputerADCInertial Reference UnitIRUHead-Up Display Unit (“Glass-cockpit” Display)HUDUDigital ComputerDC(Mission Computer)(MC)Display Unit(DU)(Mission Computer Display)(MCD)Data Entry KeyboardDEK(Mission Computer Keyboard)(MCK)Intercommunications Set ControlICSCIntercommunications stationno acronymAudio Frequency Amplifierno acronymPublic Address Set Controlno acronymCordless Headsetno acronymRadio Receiver-Transmitterno acronymCargo Winch Remote Controlno acronymBattery Chargerno acronymCommunication-Navigation Equipment ControlCNECCommunications Equipment ControlCECCentral Aural Warning ComputerCAWCWarning And Caution ComputerWACCWarning and Caution Annunciator PanelWACAPSignal Data ConverterSDCCoder Decoder Keying DeviceCDKDTransponder Set Test Setno acronym(I-Band Transponder Test Set)(TTU)Satellite Data UnitSDUCommunications Management UnitCMUSignal Acquisition UnitSAU
Aircraft such as the C-17 include a variety of actuators and sensors that provide output signals of flight conditions or vehicle health/state that can be monitored and recorded during operation. Many sensors and their outputs are not associated with an LRU, including electrical and electo-mechanical actuators, valves, transducers, sensors and the like.
Typically, in modern aircraft, the LRU's and other components are monitored to ensure proper operation of the aircraft. For example, onboard computing systems receive output data from a number of LRU's and other components over a Mil-Std-1553 data bus or Aeronautical Radio, Inc. (ARINC) standard 429 data bus. The output data can then be analyzed using Boolean logic diagrams, decision tables and other related methods. Evolving requirements for improved monitoring to reduce supportability costs and enhance safety, however, are putting new demands on current systems and methods of design. New functions are being specified that must smartly monitor subsystems and flight state, and make time-critical decisions. The size and complexity of these systems will continue to grow to achieve the cost and safety goals.
Traditional methods of monitoring and testing LRU's using production rules, logic diagrams, and decision tables work well for problems of limited size, but often have difficulty meeting requirements for complex systems including a large number of LRU's. In particular, the ability to completely verify and validate decision logic for large systems becomes a critical issue. Additionally, the types of decisions that future control systems must make will be based on expert safety strategies, as well as physical system parameters. Thus, future systems will most likely be required to rapidly recall previously captured knowledge depending upon existing conditions that are defined by large numbers of state parameters.